A one-way film has a film of a white base material on one side of which a layer of light-shielding color, such as black, is attached. The base material is perforated with lots of through-holes over the whole area thereof. When the film is attached on a window glass of a room or car, the side opposite to the light-shielding colored layer can be seen from the side of the light-shielding colored layer through the window glass; however it is difficult to see the side opposite to the white base material from the side of the white base material. In some of such one-way vision film, an image is printed on the white base material in order to provide a decorative effect.
The one-way vision film has two types, one of which is attached onto the inside of a window glass (inside attachable type) and the other of which is attached onto the outside of a window glass (outside attachable type). In order to attach the film onto a window glass after printing an image, it is necessary to form an adhesive layer on either the printed surface or the surface opposite to the printed surface.
In the outside attachable type film, the adhesive layer is formed onto the surface opposite to the printed surface. Since the film of the type is directly exposed to sun or wind and water or suffers mechanical irritation easily, a pressure-sensitive adhesion is used as an adhesion means in view of durability. So, the one-way vision film of the outside attachable type has a four-layer structure comprising a white base material; a print ink receptive layer formed onto the one side of the white base material; a light-shielding colored layer formed on the other side of the white base material; and a pressure-sensitive adhesive layer formed onto a surface of the light-shielding colored layer. And, at distribution, a backing liner is formed to protect the pressure-sensitive adhesive layer.
Furthermore, in order to obtain a required light stability, it is necessary to subject the film to a laminating for blocking an ultraviolet ray after printing an image onto the ink receptive layer. And, since the through-holes are exposed to an outside environment, dust is easily deposited on the through-holes and therefore the film become dirty in a short period of time and also is difficult to be cleaned. From this point, the laminating is required. Furthermore, when the film of the outside attachable type is applied to a tall building and the like, it is required to set up scaffolding, resulting in requirement of time-consuming works. And, when the film is seen from the outside, a problem is caused that a transparency inherent in a glass is hardly given. From these reasons, the film of the outside attachable type is not recommended.
On the contrary, the film of the inside attachable type is a film in which the adhesive layer is formed onto a side of the printed layer. Some of the film of the type has a four-layer structure comprising a white porous base material; a light-shielding colored layer formed onto one side of the base material; an ink receptive layer formed onto the other side of the base material; and a both-side pressure-sensitive adhesive film which is formed by a laminating after printing an image onto the ink receptive layer. This type requires a laminating equipment for forming the adhesive film. In addition, since an adhesive of the adhesive film penetrates through the through-holes to be exposed to an interior of the room, a dust problem in which dust is easily attached occurs.
Alternatively some of the film of the inside attachable type has a four-layer structure comprising a transparent porous base material on one side of which a pressure-sensitive adhesive layer is formed; an ink receptive layer formed onto the other side of the base material; a white layer which is formed after printing a reflected image onto the ink receptive layer; and a light-shielding colored layer formed onto the white layer. This type requires an after processing for forming the light-shielding colored layer onto the white layer. In addition, this type further requires equipments such as a screen printer for laminating the white layer and the light-shielding colored layer and the like.
As a film of the inside attachable type, a four-layer one-way vision film using a transparent resin film into which a sublimation dye can be diffused is disclosed for example, Japanese patent application 2001-334800, in which a white layer and a light-shielding colored layer are laminated onto one side of the transparent resin film in the order and an adhesive layer is formed onto the other side. By laying a transfer paper, onto which an image is printed by using an ink containing a sublimation dye, on the light-shielding colored layer and then heating the both with contacting each other closely, the sublimation dye permeates the light-shielding colored layer and the white layer so as to dye the transparent resin film The dyed transparent resin film can be seen from the side of the adhesive layer, allowing attaching the film from the inside.
In order to form the image, the producing method of the disclosed film requires a printing process for printing the image onto the transfer paper previously and a transfer process for thermal-transferring the image onto the transparent resin film. In addition, a thermal-transferring apparatus and a sublimation transferring equipment are required, causing problems in economical efficiency and marketability.
Furthermore, another method is disclosed for example, Japanese patent application 2005-14371, in which a printing sheet made of soft polyvinyl chloride is backed with a carrier sheet and then three layers of a color image layer of cyan, magenta, yellow and black; a white layer; and a black layer are thermal-transferring printed onto the other side of the printing sheet by using a thermal transfer ink ribbon. In this method, if a part of the printing sheet is made to be transparent and an adhesive layer is formed onto the carrier sheet, the method, can be applied to form a one-way vision film of the inside attachable type. And, this method does not require a perforating process, causing less working process.
This method requires a ribbon thermal transferring printer which is higher in cost than an ink-jet printer The ribbon thermal transferring printer has problems of low resolution and unable to widen the printing width. In addition, a running cost of image printing is comparatively high in cost than an ink-jet printer. And, an overprinting process is required in order to give sufficient light-shielding performance to the white layer and the light-shielding colored layer. This leads to a problem of rising cost.
Furthermore, according to result of the search carried out by the prior-art search institution recommended by Japanese Patent Office, a one-way graphic product of the inside attachable type is listed as comparison (referring to Published Japanese translations of PCT international publication 2002-518217). The published graphic product comprises a transparent porous film layer provided with a porous adhesive layer on the surface; and a non-porous colorant transferable film layer containing a detachable carrier film provided with at least one of a colored layer on the surface
The graphic product has six to seven layers containing a liner, a carrier film and the like, causing increasing of processing steps.